Fix check_untyped_defs errors in doctest

In order to make the LiteralOutputChecker lazy initialization more
amenable to type checking, I changed it to match the scheme already used
in this file to lazy-initialize PytestDoctestRunner.

src/_pytest/doctest.py

@@ -6,8 +6,12 @@ import sys
 import traceback
 import warnings
 from contextlib import contextmanager
+from typing import Dict
+from typing import List
+from typing import Optional
 from typing import Sequence
 from typing import Tuple
+from typing import Union
 
 import pytest
 from _pytest import outcomes
@@ -20,6 +24,10 @@ from _pytest.outcomes import Skipped
 from _pytest.python_api import approx
 from _pytest.warning_types import PytestWarning
 
+if False:  # TYPE_CHECKING
+    import doctest
+    from typing import Type
+
 DOCTEST_REPORT_CHOICE_NONE = "none"
 DOCTEST_REPORT_CHOICE_CDIFF = "cdiff"
 DOCTEST_REPORT_CHOICE_NDIFF = "ndiff"
@@ -36,6 +44,8 @@ DOCTEST_REPORT_CHOICES = (
 
 # Lazy definition of runner class
 RUNNER_CLASS = None
+# Lazy definition of output checker class
+CHECKER_CLASS = None  # type: Optional[Type[doctest.OutputChecker]]
 
 
 def pytest_addoption(parser):
@@ -139,7 +149,7 @@ class MultipleDoctestFailures(Exception):
         self.failures = failures
 
 
-def _init_runner_class():
+def _init_runner_class() -> "Type[doctest.DocTestRunner]":
     import doctest
 
     class PytestDoctestRunner(doctest.DebugRunner):
@@ -177,12 +187,19 @@ def _init_runner_class():
     return PytestDoctestRunner
 
 
-def _get_runner(checker=None, verbose=None, optionflags=0, continue_on_failure=True):
+def _get_runner(
+    checker: Optional["doctest.OutputChecker"] = None,
+    verbose: Optional[bool] = None,
+    optionflags: int = 0,
+    continue_on_failure: bool = True,
+) -> "doctest.DocTestRunner":
     # We need this in order to do a lazy import on doctest
     global RUNNER_CLASS
     if RUNNER_CLASS is None:
         RUNNER_CLASS = _init_runner_class()
-    return RUNNER_CLASS(
+    # Type ignored because the continue_on_failure argument is only defined on
+    # PytestDoctestRunner, which is lazily defined so can't be used as a type.
+    return RUNNER_CLASS(  # type: ignore
         checker=checker,
         verbose=verbose,
         optionflags=optionflags,
@@ -211,7 +228,7 @@ class DoctestItem(pytest.Item):
     def runtest(self):
         _check_all_skipped(self.dtest)
         self._disable_output_capturing_for_darwin()
-        failures = []
+        failures = []  # type: List[doctest.DocTestFailure]
         self.runner.run(self.dtest, out=failures)
         if failures:
             raise MultipleDoctestFailures(failures)
@@ -232,7 +249,9 @@ class DoctestItem(pytest.Item):
     def repr_failure(self, excinfo):
         import doctest
 
-        failures = None
+        failures = (
+            None
+        )  # type: Optional[List[Union[doctest.DocTestFailure, doctest.UnexpectedException]]]
         if excinfo.errisinstance((doctest.DocTestFailure, doctest.UnexpectedException)):
             failures = [excinfo.value]
         elif excinfo.errisinstance(MultipleDoctestFailures):
@@ -255,8 +274,10 @@ class DoctestItem(pytest.Item):
                     self.config.getoption("doctestreport")
                 )
                 if lineno is not None:
+                    assert failure.test.docstring is not None
                     lines = failure.test.docstring.splitlines(False)
                     # add line numbers to the left of the error message
+                    assert test.lineno is not None
                     lines = [
                         "%03d %s" % (i + test.lineno + 1, x)
                         for (i, x) in enumerate(lines)
@@ -288,7 +309,7 @@ class DoctestItem(pytest.Item):
         return self.fspath, self.dtest.lineno, "[doctest] %s" % self.name
 
 
-def _get_flag_lookup():
+def _get_flag_lookup() -> Dict[str, int]:
     import doctest
 
     return dict(
@@ -340,14 +361,16 @@ class DoctestTextfile(pytest.Module):
         optionflags = get_optionflags(self)
 
         runner = _get_runner(
-            verbose=0,
+            verbose=False,
             optionflags=optionflags,
             checker=_get_checker(),
             continue_on_failure=_get_continue_on_failure(self.config),
         )
 
         parser = doctest.DocTestParser()
-        test = parser.get_doctest(text, globs, name, filename, 0)
+        # Remove ignore once this reaches mypy:
+        # https://github.com/python/typeshed/commit/3e4a251b2b6da6bb43137acf5abf81ecfa7ba8ee
+        test = parser.get_doctest(text, globs, name, filename, 0)  # type: ignore
         if test.examples:
             yield DoctestItem(test.name, self, runner, test)
 
@@ -419,7 +442,8 @@ class DoctestModule(pytest.Module):
                     return
                 with _patch_unwrap_mock_aware():
 
-                    doctest.DocTestFinder._find(
+                    # Type ignored because this is a private function.
+                    doctest.DocTestFinder._find(  # type: ignore
                         self, tests, obj, name, module, source_lines, globs, seen
                     )
 
@@ -437,7 +461,7 @@ class DoctestModule(pytest.Module):
         finder = MockAwareDocTestFinder()
         optionflags = get_optionflags(self)
         runner = _get_runner(
-            verbose=0,
+            verbose=False,
             optionflags=optionflags,
             checker=_get_checker(),
             continue_on_failure=_get_continue_on_failure(self.config),
@@ -466,24 +490,7 @@ def _setup_fixtures(doctest_item):
     return fixture_request
 
 
-def _get_checker():
+def _init_checker_class() -> "Type[doctest.OutputChecker]":
-    """
-    Returns a doctest.OutputChecker subclass that supports some
-    additional options:
-
-    * ALLOW_UNICODE and ALLOW_BYTES options to ignore u'' and b''
-      prefixes (respectively) in string literals. Useful when the same
-      doctest should run in Python 2 and Python 3.
-
-    * NUMBER to ignore floating-point differences smaller than the
-      precision of the literal number in the doctest.
-
-    An inner class is used to avoid importing "doctest" at the module
-    level.
-    """
-    if hasattr(_get_checker, "LiteralsOutputChecker"):
-        return _get_checker.LiteralsOutputChecker()
-
     import doctest
     import re
 
@@ -573,11 +580,31 @@ def _get_checker():
                     offset += w.end() - w.start() - (g.end() - g.start())
             return got
 
-    _get_checker.LiteralsOutputChecker = LiteralsOutputChecker
+    return LiteralsOutputChecker
-    return _get_checker.LiteralsOutputChecker()
 
 
-def _get_allow_unicode_flag():
+def _get_checker() -> "doctest.OutputChecker":
+    """
+    Returns a doctest.OutputChecker subclass that supports some
+    additional options:
+
+    * ALLOW_UNICODE and ALLOW_BYTES options to ignore u'' and b''
+      prefixes (respectively) in string literals. Useful when the same
+      doctest should run in Python 2 and Python 3.
+
+    * NUMBER to ignore floating-point differences smaller than the
+      precision of the literal number in the doctest.
+
+    An inner class is used to avoid importing "doctest" at the module
+    level.
+    """
+    global CHECKER_CLASS
+    if CHECKER_CLASS is None:
+        CHECKER_CLASS = _init_checker_class()
+    return CHECKER_CLASS()
+
+
+def _get_allow_unicode_flag() -> int:
     """
     Registers and returns the ALLOW_UNICODE flag.
     """
@@ -586,7 +613,7 @@ def _get_allow_unicode_flag():
     return doctest.register_optionflag("ALLOW_UNICODE")
 
 
-def _get_allow_bytes_flag():
+def _get_allow_bytes_flag() -> int:
     """
     Registers and returns the ALLOW_BYTES flag.
     """
@@ -595,7 +622,7 @@ def _get_allow_bytes_flag():
     return doctest.register_optionflag("ALLOW_BYTES")
 
 
-def _get_number_flag():
+def _get_number_flag() -> int:
     """
     Registers and returns the NUMBER flag.
     """
@@ -604,7 +631,7 @@ def _get_number_flag():
     return doctest.register_optionflag("NUMBER")
 
 
-def _get_report_choice(key):
+def _get_report_choice(key: str) -> int:
     """
     This function returns the actual `doctest` module flag value, we want to do it as late as possible to avoid
     importing `doctest` and all its dependencies when parsing options, as it adds overhead and breaks tests.

testing/test_doctest.py

@@ -839,7 +839,8 @@ class TestLiterals:
         reprec = testdir.inline_run()
         reprec.assertoutcome(failed=1)
 
-    def test_number_re(self):
+    def test_number_re(self) -> None:
+        _number_re = _get_checker()._number_re  # type: ignore
         for s in [
             "1.",
             "+1.",
@@ -861,12 +862,12 @@ class TestLiterals:
             "-1.2e-3",
         ]:
             print(s)
-            m = _get_checker()._number_re.match(s)
+            m = _number_re.match(s)
             assert m is not None
             assert float(m.group()) == pytest.approx(float(s))
         for s in ["1", "abc"]:
             print(s)
-            assert _get_checker()._number_re.match(s) is None
+            assert _number_re.match(s) is None
 
     @pytest.mark.parametrize("config_mode", ["ini", "comment"])
     def test_number_precision(self, testdir, config_mode):